1. Technical Field
The present invention relates to a method and a device for chill molding cast iron.
A method and a device for the manufacture of cast iron parts by casting in a stationary metal mold, which is lined with a layer of hardening molding material or green sand, is shown in SE-C-506508. In that arrangement, a tubular metal mold is used whereby a tubular, upwardly open space in the mold is lined using an insulating form material. Molten cast iron is filled from above in such a way that the cooling effect of the mold and lining gives a directional frontage of solidification from the lower end of the lining and upwards to a feeder volume at the top for the last of the iron to solidify.
The described method and device give excellent results for cast parts of even thickness and relatively thin walls, such as cylinder linings, but are less suitable for casting of parts with varying cross-section and more complex geometry, where the rate of cooling will vary too much between different parts of the casting. Demands for improved mechanical properties combined with good ductility means that alloyed materials, which are traditionally used for improving mechanical properties, can not be used as the workability will be reduced due to the high carbide content and casting becomes difficult due to its tendency to shrink.
A general purpose of the present invention is to provide a method and a device for chill molding cast iron parts of varying cross-sectional area and of relatively complex geometry in which the mechanical properties of the cast material is not controlled and limited by the added alloying materials alone.
A further purpose of the casting method according to the invention is to provide increased possibilities for influencing the rate of cooling of the casting, primarily through the pearlite transformation temperature range, which makes it possible to improve the mechanical properties even further. An increased rate of cooling will also increase productivity; that is, a larger number of cast parts per unit of time and production unit.
Still further, the invention fulfills and/or enables: high level environmental requirements such as low emissions of pollutants, reduced use of energy, a clean working environment, reduced use of molding material or sand, calculated per unit of weight for castings with a corresponding reduced need for depositing molding material or sand, and a significantly improved recovery of added energy.
According to the present invention, these purposes are achieved by a device for casting cast iron that includes a chill mold having outer walls and inner walls in which the inner walls are in contact with a mold. The device also includes pressurizing means or arrangements for applying a variable pressure against the outer walls of the mold. A chill mold cooling means or mechanism for variable cooling of the inner walls of said metal chill mold is also provided.
The wall thickness of the mold is chosen so that the desired rate of heat transfer for the required mechanical properties of the cast part is achieved. The mold is preferably made of molding material or green sand.
Furthermore, it is advantageous to include an hydraulic or a pneumatic press in the pressurizing means or mechanism for acting on the outer walls of the metal chill mold.
The chill mold cooling means or mechanism preferably includes a number of cooling circuits arranged in the metal chill mold, a coolant container, a heat exchanger and a coolant pump that circulates a coolant through a coolant conduit interconnecting the cooling circuits with the coolant container, the heat exchanger and the coolant pump.
These purposes are achieved according to the present invention by a method for manufacturing cast iron parts in which a metal chill mold, having outer walls and inner walls and where the inner walls are in contact with a mold, is filled with molten cast iron. The method is characterized in that pressurizing means or mechanism can apply a variable pressure against the outer walls of the metal chill mold and the chill mold cooling means can variably cool the inner walls of the metal chill mold during the cooling of the casting.
The mold is preferably made from a hardening molding material or green sand. The thickness of the walls of the mold is chosen to achieve the required rate of cooling.
The casting method allows casting of materials having a low C-equivalent, as well as materials having high levels of carbide stabilizing alloying materials to be used to obtain castings with a considerably higher flexural strength, fatigue strength and modulus of elasticity, which in all will give good mechanical properties.
By casting materials with a low C-equivalent and by adding moderate amounts of carbide stabilizing alloying materials, a strong material, virtually free of carbides and with a good machinability, can be obtained.
The casting method will also give less dimensional scatter for the casting compared to conventional green sand casting.